1. Field of the Invention
The subject invention pertains generally to the field of imaging devices, and in particular to those devices containing an amorphous silicon sensor array.
2. Background Art
Amorphous silicon two-dimensional sensor arrays are well-known devices for real time imaging of incident energy (see R. A. Street et al., "Amorphous Silicon Arrays Develop a Medical Image", IEEE Circuits and Devices, July 1993, pp. 38-42, for a general description of the structure of the arrays). Such sensor arrays are particularly advantageous for radiation imaging because they present a relatively large size image sensor array. Sensor arrays operate on the principle of integrating a charge representative of the quantity of visible light incident on the sensor. A phosphor converter A (FIG. 1) generates the visible light B from incident high energy radiation C. Such phosphor converters operate by absorbing X-ray photons to produce high energy electrons which generate electron hole pairs, which in turn form visible light when the electrons and holes recombine. Thus, the amount of visible light generated in the phosphor converter is directly related to the radiation incident on the phosphor.
Each sensor 12 in the array 10 performs two main functions. First, the sensor captures light, and second, it stores electrical charge generated by the light. When incident light is captured by the sensor, it is turned into electrons and the electrons are stored as electrical charge by the capacitance of the sensor. Discharge of this integrated charge comprises an electrical signal representative of the incident light. Accordingly, a control circuit for the sensor array is required to selectively and independently discharge each of the sensors in a manner representative of the incident light, and thus representative of the image causing the incident light which can be conveyed to an imaging apparatus such as a display screen.
In order to convey the representative electrical signal, all sensor arrays include a set of metallization lines extending out from the sensor elements in both an x- and y- direction. These metal line are, of course, connected to an external electronic control system and so there is a need for electrical connection between the metallization lines of the array and the wire communications of the external electronics.
Advancements in sensor arrays have demanded higher and higher resolutions for better quality imaging. Higher resolution essentially means smaller pixel (sensor element) sizes. As the pixel size is reduced it becomes increasingly difficult to make the necessary connections to the signal lines of external devices.
For example, a conventional device includes metallization lines for "data", "bias" or "gate" (note FIG. 1). Such a conventional device can have a pixel size of approximately 127 microns. An eight-inch by ten-inch (8".times.10") array has approximately 1500 lines in one direction and 1900 in the other direction. This is a large number of connections to make, and since they are so very close together, it becomes quite difficult to reliably accomplish in an economical and practical manufacturing process.
Present resolution demands have suggested a reduction in pixel size to approximately 60 microns--a halving of the available distance for circuit connection for each pixel from present commercial designs. Accordingly, such a pixel size would require doubling the number of lines that need to be connected so that the lines would be even much closer together than commercial embodiments. The problems in making such connections are therefore magnitudinally increased for a commercially viable sensor array with such high resolution.
The desirability and advantage of reducing the number of address lines to thereby reduce the number of required electrical connections and to expand the spacing between the address lines for improved ease of handling and connecting are readily apparent as design goals.
The present invention describes a new and improved sensor array with a reduced number of address lines which overcomes the problems of the space limitations of prior known sensor elements to provide a new sensor assembly which has increased resolution but is economically practical for conventional connection to signal processing systems and thereby economical to manufacture, and readily adaptable to a plurality of uses for sensor arrays having a variety of configurations and dimensions.